1. Field of the Invention
The present invention relates to a process for determining the presence or absence of a possibility that a vehicle is overturned laterally or sideways, based on a rolling angle and a rolling angular speed of the vehicle. The present invention also relates to an occupant protecting system including an occupant restraint means, in which it is determined whether there is a possibility of lateral overturning of a vehicle, based on a rolling angle and a rolling angular speed of the vehicle, and when it is determined that there is a possibility of lateral overturning, the occupant restraint means is operated.
2. Description of the Related Art
A process for determining whether there is a possibility of lateral overturning of a vehicle is known from Japanese Patent Application Laid-open No.7-164985. According to such process, on a two-dimensional map made using a rolling angle and a rolling angular speed of a vehicle as parameters, a lateral overturning region is established in an area where the rolling angle and the rolling angular speed are large (i.e., an area farther from an origin of the map), and a lateral non-overturning region is established in an area where the rolling angle and the rolling angular speed are small (i.e., an area including the origin), and when a hysteresis line made by plotting actual rolling angles and actual rolling angular speeds detected by sensors on the map enters into the lateral overturning region, it is determined that there is a possibility of lateral overturning of the vehicle, whereby an active roll bar is rised.
In order to calculate an initial value for detecting a rolling angle of the vehicle, or to move a threshold value line which is a boundary between the lateral non-overturning region and the lateral overturning region on the map, a lateral acceleration of the vehicle may be detected by a lateral acceleration sensor in some cases. When the vehicle has no rolling angular speed, an output of a lateral acceleration cannot be influenced by a position in which the lateral acceleration sensor has been mounted. However, when the vehicle has a rolling angular speed about a rolling center, if the lateral acceleration sensor is mounted at a position spaced apart from the rolling center, a radial acceleration about the rolling center is generated at the position corresponding to the lateral acceleration sensor by the rolling angular speed of the vehicle, and a component of such radial acceleration in a lateral direction of a vehicle body is included as an error in an output from the lateral acceleration sensor, resulting in a problem that the lateral acceleration sensor cannot detect an accurate lateral acceleration.
An occupant protecting system is known from Japanese Patent Publication No.7-112801, which includes a seat belt device provided with a seat belt pretensioner, and an air bag device, so that the operations of the seat belt device and the air bag device are selectively controlled based on four threshold value signals output in accordance with the magnitude of a vehicle speed and the lateral overturning of the vehicle.
When the vehicle is laterally overturned slowly at a smaller rolling angular speed, the occupant is moved toward the door window by the force of gravity. On the other hand, when the vehicle is laterally overturned rapidly at a larger rolling angular speed, the occupant is left within a vehicle compartment under the action of inertia, resulting in an increased distance to the door window. When an occupant restraint means which is deployed between the occupant and the door window such as an air curtain is used, the effect of the occupant restraint means is varied depending on whether the occupant is in a position closer to the door window. For this reason, in a vehicle including a plurality of occupant restraint means, it is necessary to properly control the operations of the plurality of occupant restraint means in accordance with a rolling angular speed at the time of lateral overturning of the vehicle to exhibit an optimal occupant restraining performance. When the occupant restraint means is operated with the occupant being closer to the door window, there is a possibility that such occupant restraint means interferes with the occupant when being deployed, whereby a sufficient effect cannot be exhibited.
Accordingly, it is a first object of the present invention to ensure that when it is determined whether there is a possibility of lateral overturning of a vehicle, based on a rolling angle and a rolling angular speed of the vehicle, a reduction in accuracy of detection of a lateral acceleration due to the rolling of the vehicle is suppressed to the minimum.
It is a second object of the present invention to ensure that when a vehicle including a plurality of occupant restraint means is laterally overturned, the plurality of occupant restraint means exhibit an optimal occupant restraining performance.
It is a third object of the present invention to ensure that the operation of an occupant restraint means which is deployed between an occupant and an inner surface of a side of a vehicle body is properly controlled in accordance with the behavior of the occupant within a vehicle compartment during lateral overturning of the vehicle.
To achieve the above first object, according to a first aspect and feature of the present invention, there is provided a process for determining lateral overturning of a vehicle, comprising the step of establishing a threshold value line separating a lateral overturning region farther from an origin and a lateral non-overturning region closer to the origin on a two-dimensional map made using a rolling angle and a rolling angular speed of the vehicle, so that when a hysteresis line for actual rolling angles and actual rolling angular speeds of the vehicle traverses the threshold value line from the lateral non-overturning region to the lateral overturning region, it is determined that there is a possibility of lateral overturning of the vehicle, and wherein a lateral acceleration sensor for detecting a lateral acceleration for establishing the threshold value line is disposed on a center plane of a body of the vehicle.
With the above feature, the lateral acceleration sensor for detecting the lateral acceleration is disposed on the center plane of the vehicle body and hence, even if a radial acceleration about a rolling center on the center plane of the vehicle body is generated due to the rolling of the vehicle about the rolling center, an output from the lateral acceleration sensor cannot be influenced because such radial acceleration lies on the center plane of the vehicle body. In addition, even if an acceleration is generated on a line connecting a point of contact of one of left and right wheels on the ground and the lateral acceleration sensor to each other due to the rolling of the vehicle body about the point of contact of the wheel on the ground, an error provided to the output from the lateral acceleration sensor by the radial acceleration generated due to the rolling is equalized in a case where the point of contact of the right wheel is a rolling center and in a case where the point of contact of the left wheel is a rolling center, whereby the influence to the accuracy of detection of the lateral acceleration sensor is suppressed to the minimum.
To achieve the above second object, according to a second aspect and feature of the present invention, there is provided an occupant protecting system comprising a plurality of occupant restraint means, in which a threshold value line separating a lateral overturning region farther from an origin and a lateral non-overturning region closer to the origin is established on a two-dimensional map made using a rolling angle and a rolling angular speed of a vehicle as parameters, and when a hysteresis line for actual rolling angles and actual rolling angular speeds of the vehicle traverses the threshold line from the lateral non-overturning region to the lateral overturning region, it is determined that there is a possibility of lateral overturning of the vehicle, whereby the plurality of occupant restraint means are operated, and wherein the plurality of occupant restraint means are operated selectively based on a rolling angular speed at a time when it is determined that there is the possibility of lateral overturning of the vehicle.
With the above feature, the operation and non-operation of the plurality of occupant restraint means can be switched over between a condition when the vehicle is laterally overturned slowly at a smaller rolling angular speed, causing the occupant to be moved toward a door window, and a condition when the vehicle is laterally overturned rapidly at a larger rolling angular speed, causing the occupant to be moved away from the door window, thereby exhibiting an optimal occupant restraining performance.
To achieve the second object, according to a third aspect and feature of the present invention, in addition to the second feature, the plurality of occupant restraint means are a seat belt pretensioner and an air curtain, and in a condition where the rolling angular speed is smaller, only the seat belt pretensioner is operated, and in a condition where the rolling angular speed is larger, both the seat belt pretensioner and the air curtain are operated.
With the above arrangement, when the vehicle is laterally overturned slowly due to a smaller rolling angular speed, causing the occupant to be moved toward the door window, the air curtain which is deployed along the door window is not operated and hence, it is possible to prevent the air curtain from interfering with the occupant. Moreover, the occupant can be sufficiently restrained by the seat belt pretensioner, because the vehicle is laterally overturned slowly. When the vehicle is laterally overturned rapidly due to a larger rolling angular speed, causing the occupant to be moved away from the door window, the air curtain can be operated without interfering with the occupant, and the seat belt pretensioner can also be operated, whereby the occupant can be restrained by both the air curtain and the seat belt pretensioner.
To achieve the third object, according to a fourth aspect and feature of the present invention, there is provided an occupant protecting system comprising a occupant restraint means, in which a threshold value line separating a lateral overturning region farther from an origin and a lateral non-overturning region closer to the origin is established on a two-dimensional map made using a rolling angle and a rolling angular speed of a vehicle as parameters, and when a hysteresis line for actual rolling angles and actual rolling angular speeds of the vehicle traverses the threshold line from the lateral non-overturning region to the lateral overturning region, it is determined that there is a possibility of lateral overturning of the vehicle, whereby the occupant restraint means is operated, and wherein timing of deployment of the occupant restraint means is controlled in accordance with a condition of the occupant within a vehicle compartment in a lateral direction of a vehicle body, attendant on the lateral overturning of the vehicle.
With the above arrangement, the timing of deployment of the occupant restraint means is controlled in accordance with whether the occupant is moved toward an inner surface of a side of the vehicle body or toward a central portion of the vehicle body. Therefore, it is possible to avoid such a situation that the occupant restraint means interferes with the occupant during deployment thereof between the occupant and the inner surface of the side of the vehicle body and as a result, a sufficient effect cannot be exhibited.
To achieve the third object, according to a fifth aspect and feature of the present invention, in addition to the fourth feature, the condition of the occupant is a distance between the occupant and the inner surface of the side of the vehicle body.
With the above arrangement, the timing of deployment of the occupant restraint means is controlled in accordance with the distance between the occupant and the inner surface of the side of the vehicle body and hence, it is possible to reliably prevent the occupant restraint means from interfering with the occupant during deployment thereof.
To achieve the third object, according to a sixth aspect and feature of the present invention, in addition to the fourth feature, the condition of the occupant is a relative speed between the occupant and the inner surface of the side of the vehicle body.
With the above arrangement, the timing of deployment of the occupant restraint means is controlled in accordance with the relative speed between the occupant and the inner surface of the side of the vehicle body and hence, it is possible to reliably prevent the occupant restraint means from interfering with the occupant during deployment thereof. The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.